1. Field of the Invention
This invention relates to coaxial cables, and is particularly concerned with a simple high-power coaxial cable operating at high frequency and of a construction which accommodates substantial rf heating.
2. Description of Related Art
Prior art coaxial cables transmitting high average power, e.g., in excess of 150 watts, from traveling-wave tubes operated at high frequencies, e.g., about 9 to 11 gigahertz, must allow for substantial heat generation due to dissipation of rf energy. With sufficient heating, the insulation employed in the coaxial cable will tend to become displaced and not return to its proper position, which will tend to destroy the 50-ohm characteristic impedance desired to be maintained between the center and outer coaxial conductors. In addition, burning of the insulation and melting of circuit contacts may result.
In one form of prior art coaxial cable, a fluted Teflon insulator with a center hole was employed to maintain the center and outer conductors properly spaced, but such device was ineffective to accommodate a substantial amount of heat. Teflon foam has also been used for this purpose, but it lacks structural integrity.
Further, 90.degree. turns in prior art coaxial cables have generally been made over a large radius. Sharp right angle turns are usually avoided in any rf device because impedance changes and rf heating resulting from such sharp turns are difficult to control effectively.